Lens cells utilize Na, K-ATPase to preserve stable cytoplasmic composition and thus transparency. In order to overcome the difficulty of ion regulation in such a large mass of tightly packed cells, the lens is specialized such that epithelial cells, particularly at the lens equator, maintain a high activity of Na, K-ATPase while fiber cells have low Na, K-ATPase activity. This unequal distribution of Na, K-ATPase activity is important because it provides the driving force for circulating ionic currents that flow outward at the posterior pole, inward at the anterior pole. However there is a gap in our knowledge of how the unequal spatial localization of Na, K-ATPase activity is established because all lens cells, epithelium and fibers, have a similar abundance of Na, K-ATPase protein. The level of Na, K-ATPase protein expression in lens cells does not tally with Na, K-ATPase activity. Other factors seem to be involved. Here we plan to study how the epithelial cells achieve and maintain high Na, K-ATPase activity. Studies will be conducted to examine the link between activity of Na, K-ATPase and the ability of lens epithelial cells to synthesize new Na, K-ATPase protein (Aim I); determine whether oxidative posttranslational modification of Na, K-ATPase protein contributes to reduction of Na, K-ATPase activity (Aim II); and to determine whether tyrosine phosphorylation of the a subunit can bring about changes in Na, K-ATPase activity (Aim III). Results from these studies will give us a better understanding of lens ion regulation and lens cell specializations that underpin long term maintenance of lens transparency.